Yes, I like a lot of Celtic music too, especially Altan and the Chieftains.
Of the bands you mention, the only name I recognise is Afro Celt Sound System, so I might investigate those other artists later on if I have time. I hope you´ll be telling us about some Polish/East European sounds too.
Here´s a band you may be interested in if you don´t know them already.They were recommended by an MB girl from Prague, but unfortunately she doesn´t post here any more:-
http://www.musicbanter.com/country-f...r-valravn.html
Yes, I agree with what you say about the boundaries of world music - they are so blurred that they barely exist anymore. That´s a good description; the "vertical" and the "horizontal".